Two types of memory devices are commonly used in the field of data storage. The first type is volatile memory in which stored information is lost when power is removed. The second type is non-volatile memory in which the information is preserved after the power is removed. Non-volatile memory may be designed for multiple programming or for one-time programming. Examples of multiple programmable non-volatile memory include electrically erasable programmable read only memories (EEPROMs) and flash memory. Unlike a multiple programmable memory, a one-time programmable non-volatile memory can be programmed only once. The programming typically involves the “blowing” of a fuse element of the cell. The programming of a one-time programmable memory is irreversible.
Fuse elements in typical one-time programmable memory cells are thin oxide devices. Thin oxide devices are susceptible to voltage stress, particularly as the voltage demands on these thin oxide devices also increases. Additionally, many modern applications require secure storage of large amounts of data in non-volatile memories. Because of the nature of the information required in these secure applications, the ability to output a random value on power-up and to protect stored data from alternation after programming are critical.
What is therefore needed is a one time programmable memory cell with increased manufacturability margin which also reduces the voltage stress on the thin oxide fuses.
What is further needed is a one time programmable memory cell providing random output during power up.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.